Defeating an incumbent like Pete Sessions by the margin he did in 2018 was no small feat (John Culberson barely campaigned against Lizzie Fletcher and lost by less). If he can stave off additional bleeding with Hispanic voters I think there's an argument to be made that this could be the cycle's closest Senate race, percentage-wise.
Then again, Colin underperformed Biden by 5 in 2020. He is a generic party-line gun-grabbing Democrat who has no appeal to any swing demographics, though I am not writing him off completely.